a) Field of the Invention
The present invention relates to a motor brake control circuit for reducing the time required for a motor to come to a complete stop from the initiation of braking operation.
b) Prior Art
The rotary speed of the disc-carrying turn table in a compact disc or laser disc playing apparatus needs to be reduced to as low as 30 r.p.m., for instance, or to zero r.p.m. whenever the disc is to be replaced in order to avoid any possible damage to the disc. It is desirable for a person who uses the apparatus that the time required for replacing the disc be as short as possible. A brake circuit is normally provided for a disc playing apparatus to brake the spindle motor of the apparatus with a view to meeting these requirements.
In U.S. Pat. No. 5,010,283, a motor brake control circuit is disclosed comprising a first discriminator circuit for detecting the sense of rotation of the motor by applying a rotatory signal having a value proportional to the rate of rotation of the motor, a second discriminator circuit for detecting the sense of rotation of the motor by applying a negative logic signal of the rotational signal, a sense-of rotation directing circuit for controlling the motor drive circuit and reversing the sense of rotation of the motor whenever a brake command is given to the motor and a brake circuit for turning off the power for said drive circuit whenever a change in the signals from the first and second discriminator circuits is detected for the first time after the reversal of the sense of rotation of the motor.
With a motor brake control circuit according to the above patent, the sense of rotation of the motor is detected by the first discriminator circuit from a rotational signal having a value proportional to the rate of rotation of the motor and concurrently by the second discriminator circuit from a negative logic signal of the rotational signal. The motor drive circuit is controlled by the sense-of-rotation directing circuit for reversing the sense of rotation of the motor whenever a brake command is given to the motor. The power for the motor drive circuit is turned off whenever a change in the signals from the first and second discriminator circuits is detected for the first time after the reversal of the sense of rotation of the motor. With such an arrangement, the motor is subjected to a braking force which is proportional to the force of inertia of the load applied to the motor and the power for the motor is turned off only after a period of a half cycle of the rotational signal has elapsed subsequent to the reversal of the sense of rotation of the motor caused by the brake. The net effect of such an arrangement is, therefore, a reduced time required for stopping a motor after applying the brake regardless of the level of the load being applied to the motor.
While the above arrangement has advantages as described above, additional improvements can be made. Since the brake is applied once to the motor only after a reversal in the sense of rotation of the motor is detected and then the motor is left for natural deceleration, the motor can keep rotating considerably by the force of inertia after the application of the brake.
FIGS. 5 and 6 of the accompanying drawings show the relationship between the stopping action and the time required for it of a motor comprising a motor brake control circuit according to the cited invention, where a 3.5 inch optical/magnetic disc constitutes the load applied to the motor. As can be seen from FIGS. 5 and 6, if a brake command is issued while the motor is running in a predetermined direction, the motor is braked by a force trying to drive it in the opposite direction and, as soon as the motor is detected to be actually running in the opposite direction, the power for the motor is turned off. Therefore, at the final stages of the braking operation, the motor keeps on rotating by the force of inertia of the motor itself and the load applied to it, prolonging the time required for the motor to actually come to a complete standstill.
It is therefore an object of the present invention to solve the above described technological problem by providing a motor brake control circuit that forcibly and electrically applies the braking action to the motor without leaving it to natural deceleration so that the time required for the motor to come to a complete standstill from the initiation of braking operation may be significantly reduced.